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# 22.9.4 *Nominal Shear Strength*

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If shear-friction reinforcement is perpendicular to the shear plane, nominal shear strength across the assumed shear plane shall be calculated by:

V _{n}= µA _{vf}f_{y} | (22.9.4.2) |

where *A _{vf}* is the area of reinforcement crossing the assumed shear plane to resist shear, and µ is the coefficient of friction in accordance with Table 22.9.4.2.

**Table 22.9.4.2—Coefficients of friction**

Contact surface condition | Coefficient of friction µ^{[1]} | |
---|---|---|

Concrete placed monolithically | 1.4λ | (a) |

Concrete placed against hardened concrete that is clean, free of laitance, and intentionally roughened to a full amplitude of approximately 1/4 in. | 1.0λ | (b) |

Concrete placed against hardened concrete that is clean, free of laitance, and not intentionally roughened | 0.6λ | (c) |

Concrete placed against as-rolled structural steel that is clean, free of paint, and with shear transferred across the contact surface by headed studs or by welded deformed bars or wires. | 0.7λ | (d) |

^{[1]}λ = 1.0 for normalweight concrete; λ = 0.75 for all lightweight concrete. Otherwise, λ is calculated based on volumetric proportions of lightweight and normalweight aggregate as given in 19.2.4, but shall not exceed 0.85.

If shear-friction reinforcement is inclined to the shear plane and the shear force induces tension in the shear-friction reinforcement, nominal shear strength across the assumed shear plane shall be calculated by:

V _{n}= A(µsinα _{vf}f_{y}+ cosα) | (22.9.4.3) |

where **α** is the angle between shear-friction reinforcement and assumed shear plane, and µ is the coefficient of friction in accordance with Table 22.9.4.2.

The value of

**across the assumed shear plane shall not exceed the limits in Table 22.9.4.4. Where concretes of different strengths are cast against each other, the lesser value of***V*_{n}**shall be used in Table 22.9.4.4.***f*'_{c}**Table 22.9.4.4—Maximum V_{n} across the assumed shear plane**

Condition | Maximum V_{n} | ||
---|---|---|---|

Normalweight concrete placed monolithically or placed against hardened concrete intentionally roughened to a full amplitude of approximately 1/4 in. | Least of (a), (b), and (c) | 0.2f'_{c}A_{c} | (a) |

(480 + 0.08f')_{c}A_{c} | (b) | ||

1600A_{c} | (c) | ||

Other cases | Lesser of (d) and (e) | 0.2f'_{c}A_{c} | (d) |

800A_{c} | (e) |

Permanent net compression across the shear plane shall be permitted to be added to

**, the force in the shear-friction reinforcement, to calculate required***A*_{vf}f_{y}**.***A*_{vf}Area of reinforcement required to resist a net factored tension across an assumed shear plane shall be added to the area of reinforcement required for shear friction crossing the assumed shear plane.

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